The application of coating liquids to substrates is known in the art. Factors used in determining a method of liquid application to a substrate include the interaction of the coating liquid with the substrate, the environment in which the application will take place, the nature of the substrate, e.g., solid, porous, etc., and any environmental hazard created by the carrying agent of the coating liquid.
Conventional application methods including spraying the coating liquid onto a substrate and immersing a substrate in a bath of coating liquid are known. However, spraying is not an acceptable option if the coating liquid is an environmental hazard. In addition, spraying does not always provide the high quality standards required for some applications, e.g., medical applications wherein coating liquids are coated onto a surface of a porous substrate for a medical use. In this setting, spraying may negatively affect the uniformity of the dosing of the coating liquid onto the surface of the substrate as well as the recovery rate of coating liquid. For sprayed media, the recovery rate is only 50 to 80% of sprayed media. When the media being sprayed is costly, this recovery rate could be problematic.
With regard to immersion in a bath, again there is a problem with recovery and dose uniformity. Further, this method is not viable if it is desired to coat only one side of a substrate. With further regard to immersion, it is known to use vacuum pickup of a substrate prior to immersing the substrate; however, this method is not viable if the substrate is porous.
Based on the foregoing, a need exists for an improved method of applying coating liquids to a substrate, particularly to a porous substrate, used in medical applications.